1. Field of the Invention
The present invention relates generally to a purge process for use in the production of a carboxylic acid. More specifically, the present invention relates to the use of a purge process for separating and routing various oxidation byproducts formed in a terephthalic acid production process.
2. Description of the Prior Art
In conventional terephthalic acid (TPA) production processes, para-xylene undergoes oxidation. In such processes, oxidation byproducts are produced along with the formation of TPA. Typically, such oxidation byproducts include the oxidation intermediates and side reaction products formed in the oxidation of para-xylene, as well as any impurities originating from the raw materials. Some of these byproducts are detrimental to the use of TPA in various production processes, such as for the production of polyethylene terephthalate (PET), dimethyl terephthalate (DMT), or cyclohexane dimethanol (CHDM). Accordingly, at least a portion of these detrimental oxidation byproducts are typically removed from the TPA production process in order to yield a commercially usable TPA product. On the other hand, some oxidation byproducts are not detrimental to these production processes. In fact, some oxidation byproducts, such as bi-functional compounds, are actually useful in a PET production process.
It is known in the art to employ a purge process to remove oxidation byproducts from TPA production processes, thus rendering the TPA product suitable for use in the various above-mentioned production processes. A purge process typically involves separating a portion of a mother liquor, generated from the separation of liquid from the product stream, to form a purge feed stream. The purge feed stream generally constitutes in the range of from 5 to 40 percent of the total mother liquor, but can be up to 100 percent of the mother liquor. In a typical conventional purge process, the purge feed stream contains acetic acid, catalyst, water, oxidation byproducts, and minor amounts of terephthalic acid. The purge feed stream in conventional processes is usually resolved into a catalyst rich stream and an oxidation byproduct rich stream. The catalyst rich stream is typically recycled to the oxidizer, whereas the oxidation byproduct rich stream is usually routed out of the TPA production process for waste treatment or destruction. In such a conventional process, the oxidation byproduct rich stream contains all of the different types of byproducts generated in the oxidation step. Thus, conventional purge processes expel both detrimental and non-detrimental oxidation byproducts from the TPA production process.
Accordingly, there is a need for a purge process that can differentiate detrimental oxidation byproducts from non-detrimental and/or beneficial oxidation byproducts. Such differentiation enables the operator to allow some or all of the non-detrimental and/or beneficial oxidation byproducts to exit the TPA production process along with the TPA product in order to increase product yield and decrease costs associated with waste treatment.